CA2135919A1

CA2135919A1 - Article and method for applying a temperature indicating composition

Info

Publication number: CA2135919A1
Application number: CA002135919A
Authority: CA
Inventors: Dirk Jean Van Praet
Original assignee: Individual
Current assignee: Commscope Connectivity Belgium BVBA
Priority date: 1992-05-22
Filing date: 1993-05-21
Publication date: 1993-12-09
Also published as: DK0641428T3; ATE169108T1; WO1993024816A1; EP0641428B1; US5573848A; EP0641428A1; GB9210968D0; JPH07507244A; DE69320042D1; MX9303013A; DE69320042T2

Abstract

An article is provided for applying a temperature indicating composition (8) on to the surface of a heat recoverable substrate.
The article comprises the following four layers: backing layer (2), release layer (4), indicating composition (8), heat-activatable adhesive layer (10). The conversion temperature of the temperature indicating composition (8) is higher than the melting temperature of the release layer (4) and the melting temperature of the release layer (4) is the same as or higher than the activation temperature of the adhesive (10).

Description

-` 213~919 1`~
WO 93/24816 PCI/GB93/01045 r -~~
l-''"`

Article dnd method for applying a temperature indicating composition This mvenhon relates to ar~cles and methods for applying temperature indicating compositions to heat recoverable articles. ~ ,~
1.....
Temperature indicating compositions are typically compositions which change colour on being heated to a typical, usually well-defined, temperahlre.
I~e change in colour is frequently reversible and associated with a reversible chemical change which occurs at that temperature. Such materials are discussed and reviewed, for example, in two articles by Jess He Day in chem.
R~v. 63, 65 ~1963) and Chem. Rev. 68,649 (1968).

Typically temperature indicatin~ compositions are used as warning indicators that a certain maximum safety temperature has been reached or as means whereby a subsequent check will reveal that some critical temperature was attained.

One especially interesting applica~on of temperature indicating compositions has been in ~e field of heat recoverable articles. Heat recoverable articles include heat-shrinkable polymeric sleeve described and claimed, for example, in US Pat Nos. 2,027,962; 3,086,242; 3,957,372; 3,379,218 and British Pat Nos.1,lS5,470; 1,211,988 and 1,346,479, and also heat recoverable articles based on fabrics as described for example in EP-A-0116393 (MP0790) and EP-A-01176026 (RK176) and EP-A 0116392 (RK178).
These comprise a recoverable fabric in conjunction with a polymeric matrix forIned by laminating a polymeric material to one or both sides of the fabric to render it impe~rious. Another type of heat-recoverable article is described in British Pat. No.1,440!524 in which an elastomer member such as an outer tubular member is "held out" in a stretched state by a second member~ such as an inner tubular member, which upon héating weakens and thus allows the elastomeric member to recover.
L:-`
These heat-recoverable articles are typically provided with a sealant coating, for example on the inner surface of a heat-shrinkable sleeve, so that aseal is made between the sleeve and a substTate such as a pipe or cable when the sleeYe shrinks around it. The sealants are usually mastics or hot-melt adhesives. In such cases, heat is required both to shrink the sleeve and to melt the sealant. The heating may be by an externally applied torch or may WO 93/24816 2 PCI /GB93/01045 -;
be elec~ically applied, e.g. by forming the sleeve of a conductive polymeric material, or by laminating elec~ical wires in the sleeve, as described for example in EP -158519 (B100COM EPC). Whichever heating means is used it is desirable to ensure that the sleeve does not become too hot to deteriorate it, and yet, on the other hand, it is important that sufficient heat is applied to cause the sealant to melt and flow when in contact with the substrate. It has been proposed therefore in, for example, US Pat No. 3,~i6,335; British Pat. No.
1,511,053 and US Pat No. 4344909, to use a suitable tem~3erature indicaring composition on the surface of the heat-recoverable a`Iticle in order to msnitor and control the heat during recovery.

Known tempèrature indicating compositions are typically applied using a solvent. US 4,344,909, for example, describes a temperature indicating composition comprising an organic thermochromic material, e.g. allantoin, a polymeric binder, e.g. an acrylic resin, and an organic solvent, preferably a halogenated, e.g. chlorinated, solvent such as 1,1,1 - trichloroethylene and mixtures thereof.

We have discovered that a completely different technique can usefully be employed to apply a temperature indicating composition to the surface of a heat recoverable artide. The technique uses a hot transfer process similar to that known and used in a different field of technology, that of applying a printed image to plastic bottles and ~e like.

The lcnown hot transfer process technique involve using heat and pressure to apply a printed image. Typically a heat transfer decal is produced on a wax-coated paper carrier. The word "decal" is the term used in the Art to describe a carrier on which the desired printing pattern is prelaminated. A
~ypical decal structure therefore comprises a laminate of the following sequential layers: wax coated paper, a protective lacquer, inks, and an adhesive lacquer. Heat transfer decals are applied to bottles by heating the wax coated paper layer and pressing the laminate against the substrate to be printed (e.g. a bottle). The heat melts the wax, softens the inks and tac~ifies the adhesive lacquer. Therefore the adhesive sticks to the substrate.
Generally the wax splits leaving part of itself over the ink and part on the backing paper layer, which is then discarded. These known hot transfer processes are described, for example, in chapter 14 of "Plastics Finishing and 2 1 3 S 9 1 9 ¦ r ~
wo 93/2481~ 3 pcr/Gss3/o1o45 j-Decorating" edited by Donatas Satas, published by Van Nostrand Reinhold Co (NY) 1986.

The present inven~on lies in recognising that the heat transfer processes, known and used for printing onto non-recoverable plastic substrates such as bottles, can be modified and adapted and used in the application of temperature indicating compositions to heat recoverable substrates.

A first aspect of the present invention provides an article for applying a temperature indicating composition onto the surface of a heat recoverable substrate comprising:

(i) a backing layer, (ii) a meltable release material mounted on one surface of the backing layer, (iii) a temperature indicating composition, which changes its visual ~
appearance when heated above a pre-selected temperature Tc :-(iv) a heat activatable adhesive layer for bonding the temperature indicating composition to a surface of a heat recoverable artide, wherein the temperature indicating composition is positioned between the release rnaterial and the adhesive layer, and wherein Tc is higher ~an ~e melting temperature Tm(rl) of the release material, which is, in turn, the same as, or higher than the activation temperature Ta(al) of the adhesive layer.

The second aspect of the p~esent invention provides a method of ~ I :
applying a temperature indicating composition onto the surface of a heat recoverable s~ibstrate, comprising ~-(a) positioning an article according to any preceding claim over the surface of the heat recoverable artide, wo 93/24~16 4 pcl/Gss3/olo4s (b) h2ea1tlng ~e article to a temperature of at least Ta(al) to activate the adhesive layer, and thereby secure the article to the surface of the heat recoverablesubstrate, then .
(c) heating the article to a temperature that is at least as high as Tm(rl) but is lower than Tc~ thereby releasing the ba~F g layer from the article, but not effecting the change in visual appe~rance of the temperature indicating composition. ~`~

According ~o the invention part or all of the release layer may be removed with the backing layer. Where only some is removed, a rem~ining portion may act to protect the temperature indicating composition and the adhesive.

The release material typically comprises a polymeric material. Such material may exhibit a melting temperature range on heating rather than a sharp melting temperature. Therefore for precision it is desirable to specify a particular test for determination of melting temperature. Accordingly the term "melting temperature" of the release material, as used in this specification, means the melting temperature as measured by method C2, which uses Differential Scanning Calorimetry, as described in International Standard ISO 3146. (Ref 1503146-1985 (E)).

Similarly the adhesive layer typically comprises a polymeric material.
Its activation temperature is the temperature at which it will adhere to a substrate. This temperature is typically at or close to the melting temperature of the material. It may be up to 10-20C above the melting point. ~herefore where reference is made in the present specification to activation temperature of the adhesive layer this can be defined as ~e melting temperature, as measured by ISO 3146 referenced above.
!
In the method according to the invention Ta(al) is preferably lower than Tm(rl) and step (b) preferably involves heating the article to a , temperature that is at least as high as Ta(al) but is lower than Tm(rl~ In the method pressure is preferably applied to urge the article against the substrate,simultaneously with, or subsequent to, the heating in step (b). Preferably `pressures of at least 150N/cm2 are applied. For rubber roller presses, pr~ossures in the range 150-350 N/crn2 are preferably applied. For metal WO 93/24816 - 5 - PCI /GB93/0104~
presses pressures up to about 140û N/cm2 may be applied. Heat and 3 pressure are preferably applied by the use of hot platens in a manner known ' to the man skilled in the art of hot processing techniques.

Using the invention, it is therefore possible to apply a temperature indicating composition to-a heat recoverable composition using a hot-pressing technique. The m~terials for the adhesive layer and the release layer are selected such that premature conversion of the indicating composition does not take place. As mentioned above the indicating compositions are preferably selected for recoverable articles to indicate when recovery is complete and effective melting of sealant/adhesive sleeve linings has taken place. Therefore thè indicating composition according to the invention preferably undergoes a visible change in appearance at about the recovery temperature of the recoverable substrate. Therefore, since the materials for the adhesive layer and the release layer are selected such that the process of application of the compositions does not cause premature conversion of the indicating composition, their selection automatically ensures that the process of application of the compositions similarly does not cause premature recovery of the substrate.

The temperature indicating composition of the invention may be present in the article of the invention in any convenient form. It may be a continuous layer, but more usually will be non continuous, e.g. in a pattern.
For example it may be provided as randomly or uniformly distributed series of dots, as stripes, or as alphanumeric characters, or graphics.
Advantageously, for example, information may be presented by the temperature indicating composition, e.g. the origin or size of the substrate or the like.

The release material is preferably present in the form of a continuous layer. Instead, for example, it may be provided in regions that simply cover and preferably slightly overlap the edges of the temperature indicating composition regions. In general, the release layer may be provided in any way sufficient to release the in}c when subjected to heat and pressure. t.' ' An additional, protective, material may be provided between the temperature indicating composition and the release layer. This can function to protect the temperature indicating composition once applied to the W093/24816 2135919 -6- PC'r/GB93/01045 !~
substrate and/or to protect the adhesive layer. The additional protective layer may not be advantageous, for example, where part of the release layer remains over the temperature indicating composition when the backing is released. In the latter case the remaining portion of the`release material can li provide protection for the temperature indicating com;~osition and the adhesive. It is preferably in the form of a continuous la~er, but again may simply cover the temperature indicating composit~3~'regions.

According to the invention Tc is higher than Tm(rl). Preferably Tc is at least 5C, especially at least 10C, more preferably at least 30C, especially preferably at least 50C higher than Tm(rl). This temperature dîfference provides some tolerance in the process for application of the temperature indicating composition, without risking premature conversion of the temperature indicating composition.

Also according to the invention Tm(rl) is at least as high, and is preferably higher than Ta(al). Preferably Tm(rl) is at least 5C, preferably at least 10C, more preferably at least 30C, especially preferably at least 50C
higher than Ta(al). If Tm(rl) and Ta(al) are approximately the same temperature then release of the temperature indicating composition is substantially simultaneous with its adherence to the substrate. A temperature difference between Tm(rl) and Ta(al) permits easier handling and application of the temperature indicating composition.

Turning now to the compositions of the various components of the article according to the invention, the backing layer may comprise any material able to withstand the temperatures applied to activate the adhesive and to release the release materials. Typical examples include paper or polyester. Typically the backing layer is 0.01 too 0.04 mm thick.

The release material preferably has a melting point (as hereinbefore defined) in the region 150-250C, preferably in the range 170-230C. As examples the release material may comprise a hot melt adhesive such as an ethylene vinylacrylate, waxes, resin, or polypropylene. The release material is i- -preferably a thin layer less than 20 microns thick, preferably less than 10 or even less than 5 microns thick.

~13591~
wo 93/24816 7 pcr/GB93/olo4 The adhesive layer preferably has an activation temperature (as hereinbefore defined) in the range 100-200C. Typically it is an adhesive lacquer and comprises a special polyethylene for example EVA, ethyleneco-terpolymers, modified polyamides, tacl<ified elastomeric materials (SBS, SIS, PIB, nitrile rubbers) and any other materials which give good adhesion to polyethylene). It is preferably in the form of a layer less than 20 microns thick, preferably less than 10 or even less than 5 microns thick.

The temperature indicating composition preferably undergoes a change in appearance at a temperature Tc in the range 200-300C, preferably in the range 230-270~C, especially about 250C. The change in appearance is preferably a visible colour change e.g. green to black.

The protective material, if present, is preferably in the form of a layer.
It must be able to withstand heating to temperatures greater than Tc without deleterious effect. Typically the protective layer is less than 20 microns thick, preferably less than 10 or even less than 5 microns thick. -Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:

Figure 1 is a cross-sectional view through an article according to the invention, and Figure 2a and 2b are cross-sectional views showing the article of Figure 1 being applied to a heat recoverable sleeve.

Referring now to the drawings, the article 1 of Figure 1 comprises a laminate structure comprising the following sequential layers: paper backing layer 2, hot melt EVA adhesive release layer 4, protective lacquer (query inventor) layer 6, tempera~ure indica~ng composition layer 8, and a heat activatable adhesive layer comprising special polyethylene 10. the conversion temperature Tc of the temperature indicating composition 8 is about 250C.
The melting temperature Tm(rl) of the release layer 4 is about 200C, and the activation temperature of the adhesive layer 10 is about 150C.

Figures 2a and 2b show successive stages in application of the article 1 to the surface of a heat recoverable polymeric sleeve 12. In Figure 2a the 2135919 ` ~ ~
wo 93/24816 - ~3 pcr/Gs93/o1o4s article 1 is placed adjacent the sleeve 12. In Figure 2a the article 1 is placedadjacent the sleeve 12, and a heated platen 14 pressed against the article 1 in a direction as indicated by arrow P. The platen 14 heats the article 1 to a temperature greater than 150C thereby activating the adhesive layer 10 tc) bond the temperature indicating composition 6 (and covering layers 6, 4 and 2) to the sleeve 12. Turning now to Figure 2b, further heat is then applied, either by heating platens 14 or by other means to raise the temperature above 200C (but below 250C). This melts release layer 4, so that it and the backing layer 2 can be removed by pulling, as indicated by arrow S in the drawings.
The entire release layer 4 can be removed (as shown) or the layer may split, so that part (an under part) remains over the protecting layer 6, while the remainder is removed with the backing layer 2. :

Claims

1. An article for applying a temperature indicating composition onto the surface of a heat recoverable substrate comprising:

(i) a backing layer, (ii) a meltable release material mounted on one surface of the backing layer, (iii) a temperature indicating composition, which changes its visual appearance when heated above a pre selected temperature Tc (iv) a heat activatable adhesive layer for bonding the temperature indicating composition to a surface of a heat recoverable articles, wherein the temperature indicating composition is positioned between the release material and the adhesive layer, and wherein Tc is higher than the melting temperature Tm(rl) of the release material, which is, in turn, the same as, or higher than the activating temperature Ta(al) of the adhesive layer.

2. An article according to claim 1, wherein the release material is in the form of a continuous layer.

3. An article according to claim 1 or 2, comprising a protective material positioned between the temperature indicating composition and the release material.

4. An article according to claim 3 wherein the protective material is in the form of a continuous layer.

5. An article according to any of claims 1-4, wherein Tc is at least 10°C higher than Tm(rl).

6. An article according to any of claims 1-5, wherein Tm(rl) is at least 10°C higher than Ta(al).

7. A method of applying a temperature indicating composition onto the surface of a heat recoverable substrate, comprising (a) positioning an article according to any preceding claim over the surface of the heat recoverable article, (b) heating the article to a temperature of at least Ta(al) to activatethe adhesive layer, and thereby securing the article to the surface of the heat recoverable substrate, then (c) heating the article to a temperature that is at least as high as Tm(rl) but is lower than Tc, thereby releasing the backing layer from the article, but not effecting the change in visual appearance of the temperature indicating composition.

8. A method according to claim 2 wherein Ta(al) is lower than Tm(rl) and wherein step (b) involves heating the article to a temperature that is at least as high at Ta(al), but is lower than Tm(rl).

9. A method according to claim 2 or 3, wherein pressure is applied to urge the article against the substrate, simultaneously with, or subsequent to the heating in step (b).